Optical element holding structure, optical element lens-barrel and optical communication module

0001This application claims priority from Japanese Patent Application No. 2004-343885 filed on Nov. 29, 2004 and No. 2005-073095 filed on Mar. 15, 2005, which are incorporated hereinto by reference.

BACKGROUND OF THE INVENTION

0002This invention relates to an optical element such as a lens, an optical element holding structure for holding the optical element inside a lens barrel, and to an optical-lens barrel and an optical communication module.

0003Plastic lens are often used in optical devices in view of the fact that they have the advantage of light weight and low cost. However, if temperature changes occur due to the environment in which the device is used, internal stress is generated inside the plastic lens that is supported inside the lens barrel, and the internal refractive index changes due to this stress and causes the double refraction phenomenon to occur. The internal refractive index changes can be expressed using the following formula, but the photo-elasticity index for resin is dependent on temperature as shown in <figref idref="DRAWINGS">FIG. 9</figref>, and tends to increase as the temperature increases, and thus the internal refractive index changes to a great extent due to temperature increases. <br />Internal refractive index=Amount of change in stress×photo-elasticity index

0004Patent Document 1 which is listed below discloses a lens holding structure for fixing the lens by pressing it with a ring having screws. In the case of a glass lens, stress is not generated by pressing with the ring, but in the case of a plastic lens, stress is concentrated at the area where the ring is pressed, and as described above double refraction occurs at the lens.

0005Patent Documents 2 and 3 which are listed below, each disclose a lens mechanism in which stress is applied to the outer periphery of the lens and the refractive index is changed, an imaging device that uses said lens mechanism, a lens for varying its focal length and a method for varying the focal length. However, when comparing the change in stress in the optical axis direction and that on the surface perpendicular to the optical axis, the change in stress in the optical axis direction is significantly different from the change in stress on the surface perpendicular to the optical axis, causing internal double refraction.

0006Patent Document 4 which is listed below, discloses an optical unit which uses a plastic lens having a structure in which an external force is applied to the plastic lens and the applied external force is caused to operate in the direction where the internal stress of the plastic lens is reduced, and then stress is reduced after releasing the internal stress and adjusting the optical characteristics, as well as a twist and release method and a mounting method for the plastic lens. In this optical unit, a mechanism is provided for reducing the stress on the mounting portion of the plastic lens, but this causes the optical axis to shift. In particular, when the lens undergoes repeated thermal expansion and thermal contraction due to temperature changes the optical axis shifts.

0007A conventional example of the optical communication signal transmission module that is disposed at the terminal for sending and receiving optical signals in the optical communication system formed by the optical transmission paths such as those of optical fiber is shown in <figref idref="DRAWINGS">FIG. 13</figref>. In a conventional optical communication signal transmission module <b>100</b> shown in <figref idref="DRAWINGS">FIG. 13</figref>, the optical signals from the optical transmission paths of the optical communication system are radiated from the end surface of optical fiber <b>101</b> and transmitted through a wavelength splitting filter <b>102</b> and then passed through a collimator <b>106</b> and then received at a light receiving element <b>103</b>. In addition, the optical signals from a light emitting diode <b>104</b> passes through a collimator lens <b>109</b> and is reflected at the wavelength splitting filter <b>102</b> and entered onto the end surface of the optical fiber <b>101</b>, and then sent to the optical transmission path of the optical communication system. The collimator lenses <b>106</b> and <b>109</b> are fixed inside lens barrels <b>105</b> and <b>108</b> by rings <b>107</b> and <b>110</b> respectively. The rings <b>107</b> and <b>110</b> are mounted by YAG laser welding.

0008In <figref idref="DRAWINGS">FIG. 13</figref>, the lens barrels <b>105</b> and <b>108</b> and the rings <b>107</b> and <b>110</b> are formed of metal, and the collimator lens as <b>106</b> and <b>109</b> are formed of glass. In this manner, because of the difference in the linear expansion coefficient, when the plastic lens <b>106</b> and <b>109</b> are fixed to the metal lens barrels <b>105</b> and <b>108</b>, distortion occurs between the lens <b>106</b> and <b>109</b> and lens barrels <b>105</b> and <b>109</b> due to temperature changes caused by the environment in which the optical communication transmission module <b>100</b> is used. It is to be noted that here the linear expansion coefficient of the plastic is 6.00×10⁻⁵for example, the linear expansion coefficient of the metal is for example, 1.08×10⁻⁵.

0009Stress inside the plastic lens is generated due to the above-described distortion, and furthermore the middle position of the lens sometimes shifts due to the method for fixing the lens inside the lens barrel. This shift in the middle position of the lens causes a relative shift of the middle position on the surface of the end of the optical fiber with respect to the light receiving element and the light emitting diode. For example, as shown in <figref idref="DRAWINGS">FIG. 14</figref>, if the x-axis position on the surface of the end surface of the optical fiber shifts from the center by only a few μm (same for the y-axis position), the output value rapidly decreases. In this manner, the signal-sending and signal-receiving properties of the transmission module are deteriorated by the environment in which the optical communication transmission module is used.

0010[Patent Document 1] Japanese Patent Application Laid-Open No. 6-94957 Publication

0011[Patent Document 2] Japanese Patent Application Laid-Open No. 7-159692 Publication

0012[Patent Document 3] Japanese Patent Application Laid-Open No. 9-49905 Publication

0013[Patent Document 4] Japanese Patent Application Laid-Open No. 10-186197 Publication

SUMMARY OF THE INVENTION

0014This invention was conceived in view of the above-described problems of the conventional and the object thereof is to provide an optical element in which it is possible to control the deterioration in optical properties even when there are changes in the environmental temperature and an optical element holding structure and a optical element lens barrel which limits the generation of internal stress in the optical element and controls the changes internal double refraction index with the optical element being held in the lens barrel even when temperature changes occur, and also which prevents shifting of the optical axis of the optical elements. An additional object of this invention is to provide an optical communication module using the optical element and optical element holding structure described above.

0015In order to achieve the objects described above, the optical element of this invention is made up of: an optical section having an optical function; and a stress reducing section which is positioned at the outer peripheral side of the optical section and is for reducing the stress generated when the environmental temperature changes.

0016With this optical element, when there are changes in the environmental temperature, stress generated by the changes in the environmental temperature is reduced by the stress reducing section and thus deformation of the optical section is controlled, changes in the internal refractive index is controlled, and deterioration of optical properties of the optical section is also controlled.

0017The stress reducing section in this optical element preferably is composed of an outer peripheral portion which is positioned at the outer peripheral side of the optical section and a mounting portion which protrudes from the outer peripheral portion in a direction substantially parallel to the optical axis.

0018The stress generated when the environmental temperature changes in a state where the optical element is fixed inside the lens barrel by the mounting portion is reduced by the stress reducing section and deformation of the optical section is controlled.

0019The optical element is formed from a material whose linear expansion coefficient is larger than the linear expansion coefficient of the material forming the lens barrel. Thus if for example, the material forming the optical lens is plastic, the material forming the lens barrel can be steel and the material cost and processing cost are thereby reduced.

0020It is also preferable that the outermost peripheral portion at the opposite side on the mounting portion of the outer peripheral portion is beveled as this further reduced the stress concentration on the optical section when there are temperature changes.

0021The first optical element holding structure of this invention holds an optical element including an optical section having an optical function such as a lens; an outer peripheral portion which is positioned at the outer peripheral side of the optical section and a mounting portion which protrudes from the outer peripheral portion in a direction substantially parallel to the optical axis, inside the lens barrel by bonding and fixing the holding portion that is provided inside the lens barrel so as to oppose the mounting portion.

0022With this first optical element holding structure, when the optical element is held inside the lens barrel, the mounting portion of the optical element which protrudes in a substantially parallel direction with respect to the optical axis is made to oppose the holding portion in the lens barrel and then bonded and fixed and thus even if there is a temperature change, deformation caused by temperature changes is mainly generated at the bonding surface or the mounting portion and because the optical section is disposed via the mounting portion, there is little or no deformation at the optical section which is away from the bonding surface. As a result, the generation of internal stress in the optical section is suppressed, change in the internal refractive index is controlled and deterioration in the optical properties of the optical section is controlled. In addition, because, the optical element is fixed with the mounting portion so as to oppose the holding portion in the lens barrel, shifting of the optical axis of the optical element is prevented.

0023In the first optical element holding structure, the optical element is preferably held in the lens barrel by fixing the holding portion and the mounting portion with a bonding agent. In this case, the bonding agent is preferably ultraviolet hardening resin.

0024In addition, the bonding strength between bonding surfaces of the mounting portion of the optical element and the holding portion of the lens barrel is preferably improved by being roughened using such a process as blasting.

0025Also, given that the outer diameter of the optical element is D and the distance from the surface at the opposite side of the mounting portion of the outer peripheral portion to the front end of the mounting portion is L, and the thickness of the outer peripheral portion is A, by satisfying equations (1) and (2), the deformation caused by temperature change mainly occurs at the bonding surface and the mounting portion, and little or no deformation occurs at the optical section. <br /><i>D≧</i>10×<i>A</i>  (1)<br /><i>L≧</i>2.5<i>×A</i>  (2)

0026The second optical element holding structure of this invention holds an optical element including an optical section having an optical function; an outer peripheral portion which is positioned at the outer peripheral side of the optical section and a mounting portion which protrudes from the outer peripheral portion in a direction substantially parallel to the optical axis, inside the lens barrel by fixing the mounting portion and the holding portion provided in the lens barrel with a step portion.

0027With this second optical element holding structure, when the optical element is held inside the lens barrel, the mounting portion of the optical element which protrudes in a substantially parallel direction with respect to the optical axis is fixed to the holding portion inside the lens barrel using the step portion, and thus even if there is a temperature change, deformation caused by the temperature change is mainly generated at the step portion and the mounting portion and because the optical section is disposed via the mounting portion, there is little or no deformation caused by temperature change at the optical section which is away from the step portion. As a result, the generation of internal stress in the optical section is controlled, change in the refractive index is controlled and deterioration in the optical properties of the optical section is controlled. In addition, because the optical element is fixed by the step portion in the holding portion of the lens barrel with the mounting portion, shifting of the optical axis of the optical element is prevented.

0028In the second optical element holding structure, the mounting portion of the optical element has mounting step surface, and the holding portion has a holding step surface which corresponds to the mounting step surface in the inner surface of the lens barrel, and the mounting step surface and the holding step surface are fixed so as to oppose each other. In this case, the holding ring is preferably mounted to the inner surface of the lens barrel so as to press the mounting surface at the opposite side of the mounting step surface of the optical element.

0029The third optical element holds an optical element including an optical section having an optical function; an outer peripheral portion for positioning at the outer peripheral side of the optical section and a mounting portion which protrudes from the outer peripheral portion in a direction substantially parallel to the optical axis, between a holding portion which is provided inside the lens barrel so as to oppose the mounting portion and the ring-like member which is disposed inside the lens barrel so that the protruding portion presses the outer peripheral portion which is at the opposite side from the mounting portion.

0030With this third optical element holding structure, when the optical element is held inside the lens barrel, the mounting portion of the optical element which protrudes in a substantially parallel direction with respect to the optical axis is caused to oppose the holding portion in the lens barrel and the outer peripheral portion at the side opposite to the mounting portion of the optical element is pressed in the optical axis direction by the protruding portion of the ring-shaped member that is disposed inside the lens barrel thereby held and thus even if there is a temperature change, the optical element expands substantially freely, and concentration of the stress caused by temperature change becomes difficult. As a result, generation of internal stress in the optical section is suppressed, change in the internal refractive index is controlled and deterioration in the optical properties of the optical section is controlled.

0031In the third optical element holding structure, the protruding portion of the ring-like member abuts the incline surface that is provided on the outer peripheral portion that is at the opposite side from the mounting portion. Thus, the protruding portion of the ring-like member presses the optical element to the outer side in the radial direction on the periphery of the incline surface and as a result it is difficult for the optical axis of the optical element to shift and shifting of the optical axis of the optical element is prevented.

0032The fourth optical element holding structure of this invention holds an optical element including an optical section having an optical function; an outer peripheral portion for positioning at the outer peripheral side of the optical section and a mounting portion which protrudes from the outer peripheral portion in a direction substantially parallel to the optical axis, between a holding portion which is provided inside the lens barrel so as to oppose the mounting portion and the ring-like member which is disposed inside the lens barrel so that the ring is on top of the outer peripheral portion which is at the opposite side from the mounting portion and which presses the ring.

0033With this fourth optical element holding structure, when the optical element is held inside the lens barrel, the mounting portion of the optical element which protrudes in a substantially parallel direction with respect to the optical axis is made to oppose the holding portion in the lens barrel and the outer peripheral portion at the side opposite to the mounting portion of the optical element is pressed and held in the optical axis direction with the ring-like member which is disposed inside the lens barrel via the ring which is on top of outer peripheral portion and thus even if there is a temperature change, the optical element expands substantially freely, and concentration of the stress caused by temperature change becomes difficult. As a result, the generation of internal stress in the optical section is suppressed, change in the refractive index is controlled and deterioration in the optical properties of the optical section is controlled.

0034In the fourth optical element holding structure, by disposing the ring at the rim formed in the outer peripheral portion, the ring presses the optical element to the outer side in the radial direction on the periphery of the rim and as a result it is difficult for the optical axis of the optical element to shift and shifting of the optical axis of the optical element is prevented. In this case, the ring is preferably formed of a material that is not too hard and not too soft, and fluorine resin, for example, is preferable.

0035In the third and fourth optical element holding structure, it is preferable that the holding portion protrudes inside the lens barrel from the inner surface of the lens barrel in the direction which substantially crosses the optical axis so as to abut the mounting portion of the optical section.

0036It also preferable that in the first to fourth optical element holding structures, the outermost peripheral portion at the opposite side to the mounting portion of the outer peripheral portion are beveled since this further reduces the stress concentration on the optical section when there is a temperature change.

0037In the first to fourth optical element holding structures, the optical element is formed from a material whose linear expansion coefficient is larger than that of the material forming the lens barrel. Thus if, for example, the material forming the optical lens is plastic, the material forming the lens barrel can be steel and the material cost and processing cost is thereby reduced.

0038In the first to fourth optical element holding structures, the optical element is the above-described optical element made up of an optical section having an optical function and a stress reducing section which is positioned at the outer peripheral side of the optical section and is for reducing the stress generated when the environmental temperature changes. As a result, when the optical element is fixed in the lens barrel, the stress generated by the difference in expansion and contraction between the optical element and the lens barrel due to a temperature change in the environment of use can be prevented and thus it is unlikely that this stress will be generated in the optical section. Thus deformation of the optical section of the optical element is controlled, deterioration of optical properties of the optical section is controlled and shifting of the optical axis of the optical element is prevented.

0039In the optical element lens barrel of this invention, the optical elements are held in the lens barrel by the first to fourth optical element holding structures. According to the optical element lens barrel, even if there is a temperature change in the lens barrel when the optical lens is held, generation of the internal stress in the optical section is controlled, change in the internal refractive index is controlled and shifting of the optical axis of the optical element is prevented.

0040The optical communication module of this invention includes the above-described optical element comprising an optical section having an optical function and a stress reducing section which is positioned at the outer peripheral side of the optical section and is for reducing the stress generated when the environmental temperature changes.

0041With this optical module, even if there is a temperature change in the environment in which it is being used, deformation of the optical section of the optical element is controlled, deterioration of optical properties of the optical section is controlled and shifting of the optical axis of the optical element is prevented and thus even when used in an environment where there are temperature changes, deterioration of the optical properties of the optical communication module is prevented.

0042In a separate optical communication module of this invention, the optical elements are held in the lens barrel by the first to fourth optical element holding structures.

0043With this optical communication module, even if there is a temperature change in the environment in which it is being used, deformation of the optical section of the optical element is controlled, deterioration of optical properties of the optical section is controlled and shifting of the optical axis of the optical element is prevented and thus even when used in an environment where there are temperature changes, deterioration of the optical properties of the optical communication module is prevented.

0044The bidirectional optical communication module of this invention is made up of a light emitting diode for sending optical signals to the optical fiber terminal; a light receiving element for receiving optical signals from the optical fiber terminal; a separating means for separating the first optical path between the optical fiber terminal and the light emitting diode and the second optical path between the optical fiber terminal and the light receiving element; and an optical element that is disposed between the optical fiber terminal and at least either the light emitting diode or the light receiving element, and the optical element is the above-described optical element made up of an optical section having an optical function and a stress reducing section which is positioned at the outer peripheral side of the optical section and is for reducing the stress generated when the environmental temperature changes.

0045With this bidirectional optical communication module, even if there is a temperature change in the environment in which it is being used, deformation of the optical section of the optical element is controlled, deterioration of optical properties of the optical section is controlled, and shifting of the optical axis of the optical element is prevented and thus even when used in an environment where there are temperature changes, deterioration of the signal sending and signal receiving properties of the optical communication module is controlled.

0046A separate bidirectional optical communication module of this invention is made up of a light emitting diode for sending optical signals to the optical fiber terminal; a light receiving element for receiving optical signals from the optical fiber terminal; a separating means for separating the first optical path between the optical fiber terminal and the light emitting diode from the second optical path between the optical fiber terminal and the light receiving element; and an optical element that is disposed between the optical fiber terminal and at least one of the light emitting diode and the light receiving element, and the optical element is held in the lens barrel by first to fourth optical elements.

0047With this separate bidirectional optical communication module, even if there is a temperature change in the environment in which it is being used, deformation of the optical section of the optical element is controlled, deterioration of optical properties of the optical section is controlled, and shifting of the optical axis of the optical element is prevented and thus even when used in an environment where there are temperature changes, deterioration of the signal sending and signal receiving properties of the optical communication module is suppressed.

0048In the optical elements of this invention, even if there are changes in the environmental temperature, deterioration of the optical properties is limited.

0049Also in the optical element holding structure and optical element lens barrel of this invention, even there is a temperature change when the optical element is held in the lens barrel, generation of internal stress in the optical section is suppressed and change in the internal refractive index is controlled and thus deterioration in optical properties can be controlled and shifting of the optical axis of the optical element is prevented.

0050Even when this optical communication module is used in an environment where there are temperature changes, deterioration of the signal sending and signal receiving properties of the optical communication module is suppressed.

BRIEF DESCRIPTION OF DRAWINGS

0051<figref idref="DRAWINGS">FIG. 1</figref> is an essential part vertical cross-sectional view showing the first embodiment of lens holding structure;

0052<figref idref="DRAWINGS">FIG. 2</figref> is an essential part vertical cross-sectional view showing the second embodiment of lens holding structure;

0053<figref idref="DRAWINGS">FIG. 3</figref> is an essential part vertical cross-sectional view showing the third embodiment of lens holding structure;

0054<figref idref="DRAWINGS">FIG. 4</figref> is an essential part vertical cross-sectional view showing the forth embodiment of lens holding structure;

0055<figref idref="DRAWINGS">FIG. 5</figref> is a view showing an example of lens

0056<figref idref="DRAWINGS">FIG. 6</figref> is a figure showing a deformation of entire lens in an example where the lens is fixed by adhesive at a temperature of approx. 70° C. and then the temperature returns to normal temperature (25° C.);

0057<figref idref="DRAWINGS">FIG. 7</figref> is a figure indicating a distribution of refraction rate change (stress) in the plastic lens of <figref idref="DRAWINGS">FIG. 6</figref> at each temperature (−40° C., 25° C. and 85° C.) by color.

0058<figref idref="DRAWINGS">FIG. 8</figref> is a figure indicating a distribution of refraction rate change and internal stress generated in the plastic lens of <figref idref="DRAWINGS">FIG. 6</figref> at each temperature (−40° C., 25° C. and 85° C.) by values corresponding to the colors;

0059<figref idref="DRAWINGS">FIG. 9</figref> is a graph showing a temperature relativity of optical elastic coefficient of various kinds of resins (extraction from “The property of transparent resin Olefin Maleimide Copolymer” by Yokkaichi laboratory of Touosou Co., Ltd.);

0060<figref idref="DRAWINGS">FIG. 10</figref> is a pattern diagram of the inside of a bi-directional optical communication module of the fifth embodiment viewed from the side surface;

0061<figref idref="DRAWINGS">FIG. 11</figref> is a pattern diagram of the inside of a bi-directional optical communication module of the sixth embodiment viewed from the side surface;

0062<figref idref="DRAWINGS">FIG. 12</figref> is a graph showing a relation between an optical path difference and a radius position from the center of a lens when the temperature of the plastic lens of <figref idref="DRAWINGS">FIG. 5</figref> in an example is at each temperature (−40° C., 25° C. and 85° C.);

0063<figref idref="DRAWINGS">FIG. 13</figref> is a pattern diagram of the inside of a conventional bidirectional optical communication module viewed from the side surface; and

0064<figref idref="DRAWINGS">FIG. 14</figref>. is a graph showing an example of a relation between a position in X-axis on the plane of an optical fiber terminal and an output value.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

0065The following is a description of the preferred embodiments of this invention using the drawings.

First Embodiment

0066<figref idref="DRAWINGS">FIG. 1</figref> is a main part vertical portion showing the lens holding structure of the first embodiment. The lens holding structure shown in <figref idref="DRAWINGS">FIG. 1</figref> fixes and holds a lens <b>10</b> onto the inner surface <b>20</b><i>a </i>of a cylindrical lens barrel <b>20</b> using a bonding agent.

0067The lens <b>10</b> is made up of a lens portion <b>11</b> which has a lens function; an outer peripheral portion <b>13</b> which is positioned on the outer peripheral side of the lens portion <b>11</b> and extends to the outermost periphery <b>14</b> of the lens <b>10</b>; and a mounting portion <b>12</b> which protrudes from the outer peripheral portion <b>13</b> in a direction substantially parallel to the optical axis p, and is a plastic lens which is formed from a resin for optical elements. The lens <b>11</b> has a convex portion <b>11</b><i>a </i>which is the center of the optical axis p, and the flat surface <b>11</b><i>b </i>which at the opposite side of the convex portion <b>11</b><i>a </i>extends from the lens portion <b>11</b> to a part of the outer peripheral portion <b>13</b>. The stress reducing section is formed from the outer peripheral portion <b>13</b> and the mounting portion <b>12</b>.

0068The mounting portion <b>12</b> extends so as to form a leg portion which has a substantially rectangular cylindrical configuration at the opposite side from a convex portion <b>11</b><i>a</i>, and the outer periphery which opposes the inner surface <b>20</b><i>a </i>of the lens barrel <b>20</b> forms the outermost periphery <b>14</b> of the lens <b>10</b> and inclines and with respect to the optical axis p, and extends from the outermost periphery of a flat surface <b>11</b><i>b </i>at the opposite surface (inner surface) side of the outermost periphery <b>14</b>. The front end portion of the mounting portion <b>12</b> has a mounting surface <b>15</b> which is formed in the direction which crosses the optical axis p.

0069The outer peripheral portion <b>13</b> has a concave portion <b>13</b><i>a </i>whose inner peripheral side which contacts the convex portion <b>11</b><i>a </i>is formed inwards at the convex portion <b>11</b><i>a </i>side of the lens portion <b>11</b>, and a convex portion <b>13</b><i>b </i>which is a protrusion of the outer peripheral side of the concave portion <b>13</b><i>a</i>. The corner portion of the outermost periphery <b>14</b> side of the convex portion <b>13</b><i>b </i>is beveled to form a beveled portion <b>16</b>. The beveled portion <b>16</b> may also be formed as a bent surface configuration.

0070The lens barrel <b>20</b> is made up of a holding portion <b>21</b> which is formed so as to protrude in a collar-like configuration from the inner surface <b>20</b><i>a </i>in the direction crossing the optical axis p (the radial direction inner side of the lens barrel <b>20</b>). The collar-like holding surface <b>22</b> of the holding portion <b>21</b> is formed so as to oppose the mounting surface <b>15</b> of the mounting portion <b>12</b> of the lens <b>10</b>. The lens barrel <b>20</b> is preferably formed from a metallic material such as steel or alloys of iron, nickel or cobalt (such as Kovar (trade name)).

0071In the case where the lens <b>10</b> is mounted and held in the lens barrel <b>20</b>, the lens <b>10</b> is inserted into the lens barrel <b>20</b> from the upper side of <figref idref="DRAWINGS">FIG. 1</figref> with the mounting portion <b>12</b> at the lower side thereof. At this time by applying a bonding agent in advance to at least one of the mounting surface <b>15</b> and the holding surface <b>22</b> a bonding agent layer <b>29</b> is formed between the mounting surface <b>15</b> and the holding surface <b>22</b>. In the case where an epoxy type ultraviolet hardening substance is used as the bonding agent, the bonding agent layer may be hardened by radiating ultraviolet light after inserting the lens <b>10</b> into the lens barrel <b>20</b>.

0072Due to the above described configuration, the lens <b>10</b> is fixed and held on the holding portion <b>21</b> in the lens barrel <b>20</b> by a bonding agent layer <b>29</b> using the mounting portion <b>12</b>. However because of the lens holding structure of <figref idref="DRAWINGS">FIG. 1</figref>, even if there is a temperature change due to the environment in which the device is being used, deformation of the lens barrel <b>20</b> caused by temperature changes is mainly generated at the bonding agent layer <b>29</b> and the mounting portion <b>12</b> and thus the force caused by the temperature change can be reduced. Because the lens portion <b>11</b> is disposed via the mounting portion <b>12</b> and is away from the bonding agent layer <b>29</b>, there is little or no deformation caused by the temperature change. In this manner the internal stress generated at the lens portion <b>11</b> is suppressed and change in the internal refractive index can be controlled. Furthermore because the lens <b>10</b> is fixed by the bonding agent layer <b>29</b> so as to oppose the holding portion <b>21</b> in the lens barrel <b>20</b> using the mounting portion <b>12</b> shifting of the optical axis of the lens <b>10</b> is prevented.

0073The mounting surface <b>15</b> of the mounting portion <b>12</b> of the lens <b>10</b> and the holding surface <b>22</b> of the holding portion <b>21</b> of the lens barrel <b>20</b> are preferably roughened by being subjected to blast processing for example as this improves the bonding strength between the bonding surfaces of the mounting surface <b>15</b> and the holding surface <b>22</b>.

0074It is to be noted that bonding agent is not applied between the outer most periphery <b>14</b> of the lens <b>10</b> and the inner surface <b>20</b><i>a </i>of the lens barrel <b>20</b>. Also the outer diameter of the outermost periphery <b>14</b> of the lens <b>10</b> is made smaller than the inner diameter of the lens <b>20</b> such that the lens <b>10</b> can be loosely fit into the lens barrel <b>20</b>.

0075Due to the above described configuration, even if stress is generated by the deformation of the lens <b>10</b> as a result of temperature changes in the lens holding structure of <figref idref="DRAWINGS">FIG. 1</figref>, because the length in the direction of the optical axis p of the mounting portion <b>12</b> which has a rib-like configuration is long, most of the stress is concentrated at the bonding agent layer which is between the mounting surface <b>15</b> and the holding surface <b>22</b>. Thus the bonding layer <b>29</b> and the entire mounting portion <b>12</b> deforms to a large extent and so the mounting portion <b>12</b> needs to have a prescribed length in the direction of the optical axis p.

0076Namely, as shown in <figref idref="DRAWINGS">FIG. 1</figref> given that the distance between the concave portion <b>13</b><i>a </i>of the outer peripheral portion <b>13</b> and the mounting surface <b>15</b> of the mounting portion <b>12</b> is L; the thickness of the concave portion <b>13</b><i>a </i>of the outer peripheral portion <b>13</b> is A; and the outer diameter of the lens <b>10</b> is D, by setting each of the dimensions so as to satisfy equations (1) and (2), there is a great amount of deformation of the bonding agent layer <b>29</b> and the entire mounting portion <b>12</b>. Thus it is unlikely that the lens portion <b>11</b> will deform and stress will be generated. <br /><i>D</i>≧10<i>×A</i>  (1)<br /><i>L</i>≧2.5<i>×A</i>  (2)

0077In <figref idref="DRAWINGS">FIG. 1</figref> bonding agent is used for bonding and fixing the mounting portion <b>12</b> of the lens <b>10</b> to the holding portion <b>21</b> of the lens barrel <b>20</b>, but the invention is not limited thereto, and various bonding methods such as solvent adhesion, depositing (thermal bonding), ultrasonic bonding, and welding.

Second Embodiment

0078<figref idref="DRAWINGS">FIG. 2</figref> is a main part vertical portion showing the lens holding structure of the second embodiment. The lens holding structure shown in <figref idref="DRAWINGS">FIG. 2</figref> fixes and holds a lens <b>30</b> onto an inner surface <b>4</b>.<b>0</b><i>a </i>of a lens barrel <b>40</b> using a step structure.

0079As shown in <figref idref="DRAWINGS">FIG. 2</figref>, compared to the lens <b>10</b> of <figref idref="DRAWINGS">FIG. 1</figref>, the lens <b>30</b> is has substantially the same structure as that of <figref idref="DRAWINGS">FIG. 1</figref> except for the fact that the mounting portion protrudes from the outer peripheral portion <b>13</b> in the direction substantially-parallel to the optical axis p has a step portion <b>36</b> which protrudes further out than the outermost periphery <b>14</b> of the lens <b>30</b> at the lower side that is opposite to the convex portion <b>11</b><i>a </i>of the lens portion <b>11</b>. As a result, the parts that are the same have been assigned the same numbers and descriptions thereof have been omitted.

0080In addition the lower portion in <figref idref="DRAWINGS">FIG. 2</figref> of the inner surface <b>40</b><i>a </i>of the lens barrel <b>40</b> is formed at an inner surface portion <b>41</b> having an inner diameter that is larger than that of the inner surface <b>40</b><i>a</i>, and a step portion <b>41</b><i>a </i>is formed between the inner surface <b>40</b><i>a </i>and the inner surface portion <b>41</b>. The inner surface portion <b>41</b> of the lens barrel <b>40</b> corresponds to the step portion <b>36</b> of the lens <b>30</b> and the step surface <b>41</b><i>a </i>corresponds to the step surface <b>36</b><i>a </i>of the step portion <b>36</b>.

0081A holding ring <b>42</b> disposed in the lens barrel <b>40</b> on the inner surface portion <b>41</b>, from lower part of <figref idref="DRAWINGS">FIG. 2</figref> and the end surface <b>43</b> of the holding <b>42</b> is made to contact and press the mounting surface <b>35</b> of the step portion <b>36</b> of the lens <b>30</b> and the step portion <b>36</b> of the lens <b>30</b> is thereby fixed so as to be nipped between the step surface <b>41</b><i>a </i>and the end surface <b>43</b>.

0082In the case where the lens <b>30</b> is mounted and held in the lens barrel <b>40</b>, the lens <b>30</b> is inserted into the lens barrel <b>40</b> from the lower side of <figref idref="DRAWINGS">FIG. 2</figref> with the convex portion <b>11</b><i>a </i>at the upper side thereof, and the step surface <b>36</b><i>a </i>of the step portion <b>36</b> of the lens <b>30</b> abuts the step surface <b>41</b><i>a </i>of the lens barrel <b>40</b>. In addition, the holding ring <b>42</b> is inserted onto the inner surface portion <b>41</b> of the lens barrel <b>40</b> from the lower side of <figref idref="DRAWINGS">FIG. 2</figref>, and the end surface <b>43</b> of the front end contacts and presses on the mounting surface <b>35</b> of the lens <b>30</b>. In this state, the holding ring <b>42</b> is fixed to the inner surface portion <b>41</b> of the lens barrel <b>40</b> by a bonding agent, ultrasonic wave fusion or by fitting or the like.

0083Due to this configuration, the step portion <b>36</b> of the mounting portion <b>32</b> of the lens <b>10</b> is fixed by being nipped between the step surface <b>41</b><i>a </i>in the lens barrel <b>40</b> and the end surface <b>43</b> of the holding ring <b>42</b> that was inserted and the lens <b>30</b> is thereby held inside the lens barrel <b>40</b>. With the lens holding structure of <figref idref="DRAWINGS">FIG. 2</figref>, if there is a temperature change due to the environment in which the device is used, deformation of the lens barrel <b>40</b> caused by the temperature change is mainly generated at the step portion <b>36</b> and the mounting portion <b>32</b> and stress caused by temperature change is reduced. Because the lens portion <b>11</b> is disposed via the mounting portion <b>32</b> and is away from the step portion <b>36</b>, there is little or no deformation caused by temperature change. In this manner, the generation of internal stress in the lens portion <b>11</b> of the lens <b>30</b> is suppressed and change in the refractive index is controlled. In addition, because, the lens <b>30</b> is fixed in the lens barrel <b>40</b> at the step portion <b>36</b> using the step structure, shifting of the optical axis of lens <b>30</b> is prevented.

0084It is to be noted that the outer diameter of the outermost periphery <b>14</b> of the lens <b>30</b> is made smaller than the inner diameter of the inner surface <b>40</b><i>a </i>of the lens barrel <b>40</b> so that the lens <b>30</b> can be loosely fit into the inner surface <b>40</b><i>a </i>of the lens barrel <b>40</b>.

0085As described above, in the lens holding structure of <figref idref="DRAWINGS">FIG. 2</figref>, even if stress is generated by the deformation of the lens <b>30</b> caused by a temperature change, because the length in the direction of the optical axis p of the mounting portion <b>32</b> which has a rib-like configuration is long, most of the stress is concentrated on the step portion <b>36</b> at the lower end side of the mounting portion <b>32</b>. Thus the step portion <b>36</b> and the entire mounting portion <b>32</b> deforms to a large extent and so the mounting portion <b>32</b> needs to have a prescribed length in the direction of the optical axis p.

Third Embodiment

0086<figref idref="DRAWINGS">FIG. 3</figref> is a main part vertical portion showing the lens holding structure of the third embodiment. The lens holding structure shown in <figref idref="DRAWINGS">FIG. 3</figref> holds a lens <b>50</b> onto the inner surface <b>60</b><i>a </i>of a cylindrical lens <b>60</b> using the ring-like member <b>65</b>.

0087The lens <b>50</b> is made up of a lens portion <b>51</b> which has a lens function; an outer peripheral portion <b>53</b> which is positioned on the outer peripheral side of the lens portion <b>51</b> and extends to the outermost periphery <b>54</b> of the lens <b>50</b>; and a mounting portion <b>52</b> which protrudes from the outer peripheral portion <b>53</b> in a direction substantially parallel to the optical axis p, and is a plastic lens which is formed from a resin for optical elements. The lens <b>51</b> has a convex portion <b>51</b><i>a </i>which is the center of the optical axis p and a flat surface <b>51</b><i>b </i>which at the opposite side from the convex portion <b>51</b><i>a </i>extends from the lens portion <b>51</b> to a part of the outer peripheral portion <b>53</b>.

0088The mounting portion <b>52</b> extends so as to form a leg portion which has a substantially square cylindrical configuration from the convex portion <b>51</b><i>a </i>to the opposite side, and the outer periphery which opposes the inner surface <b>60</b><i>a </i>of the lens barrel <b>60</b> forms the outermost periphery <b>54</b> of the lens <b>50</b> and inclines and with respect to the optical axis p, and extends from the outermost periphery of the flat surface <b>51</b><i>b </i>at the opposite surface (inner surface) side of the outermost periphery <b>54</b>. The front end portion of the mounting portion <b>52</b> has a mounting surface <b>55</b> which is formed in the direction which crosses the optical axis p.

0089The outer peripheral portion <b>53</b> has a convex portion <b>53</b><i>a </i>whose inner periphery side which contacts the convex portion <b>51</b><i>a </i>is formed inwards at the convex portion <b>51</b><i>a </i>side of the lens portion <b>51</b> and a convex portion <b>53</b><i>b </i>which is a protrusion of the outer peripheral side of the concave portion <b>53</b><i>a</i>. The side of the outermost periphery <b>54</b> of the convex portion <b>53</b><i>b </i>is beveled at the corner to form a beveled portion <b>56</b>. The beveled portion <b>56</b> may also have a bent surface configuration.

0090The lens barrel <b>60</b> comprises a holding portion <b>61</b> which is formed so as to protrude as a collar-like configuration from the inner surface <b>60</b><i>a </i>in the direction crossing the optical axis p (the radial direction inner side of the lens barrel <b>60</b>). The collar-like holding surface <b>62</b> of the holding portion <b>61</b> is formed so as to oppose the mounting surface <b>55</b> of the mounting portion <b>52</b> of the lens <b>50</b>. The lens barrel <b>60</b> is preferably formed from a metallic material such as steel, or alloys of iron, nickel and cobalt (such as that commercially available as Kovar).

0091A metal ring member <b>66</b> is disposed on the inner surface <b>60</b><i>a </i>of the lens barrel <b>60</b> in the upper portion in <figref idref="DRAWINGS">FIG. 3</figref> of lens <b>50</b>, and the ring-shaped member <b>65</b> has a ring-shaped protruding portion <b>66</b> at the inner peripheral side thereof. The protruding portion <b>66</b> contacts an incline surface <b>53</b><i>c </i>that is formed at the outer peripheral side of the concave portion <b>53</b><i>a </i>of the outer peripheral part of the lens <b>50</b>.

0092In the case where the lens <b>50</b> is mounted and held in the lens barrel <b>60</b>, the lens <b>50</b> is inserted into the lens barrel <b>60</b> from the upper side of <figref idref="DRAWINGS">FIG. 3</figref> with the mounting portion <b>52</b> at the lower side thereof, and abuts the holding surface <b>62</b> of holding portion <b>61</b> of the lens barrel <b>60</b>. Next, the lens <b>50</b> is inserted into lens barrel <b>60</b> so as to fit onto the ring-like member <b>65</b> from the top of <figref idref="DRAWINGS">FIG. 3</figref>, and the protruding portion <b>66</b> of the ring-like member <b>65</b> contacts and presses on the incline surface <b>53</b><i>c </i>of the outer periphery <b>53</b> of the lens <b>50</b>.

0093Due to this configuration, the lens <b>50</b> can be held between the holding member <b>61</b> of the lens barrel <b>60</b> and the ring-like member <b>65</b>, but due to the lens holding structure of <figref idref="DRAWINGS">FIG. 3</figref>, even if there is a temperature change due to the environment in which the lens barrel <b>60</b> is used, because the lens <b>50</b> is only pressed by the ring-like member <b>65</b> from the upper portion of the drawing, the lens <b>50</b> expands substantially freely due to the temperature change, and concentration of the stress caused by temperature changes on the lens portion <b>51</b> becomes unlikely and internal stress generated due to temperature changes is reduced. In this manner, generation of internal stress at the lens portion <b>51</b> is suppressed and change in the internal double refraction index is controlled.

0094In addition, the incline surface <b>53</b><i>c </i>needed for construction of cast and mold when manufacturing the lens <b>50</b> is used to press onto the protruding portion <b>66</b> of the ring-like member <b>65</b> and thus even if there is a temperature change, shifting of the optical axis of the lens <b>50</b> in the lens barrel <b>60</b> is prevented.

0095It is to be noted that the outer diameter of the outermost periphery <b>14</b> of the lens <b>10</b> is smaller than the inner diameter if the lens barrel <b>20</b> so that the lens <b>10</b> can be loosely fit into the lens barrel <b>20</b>.

Fourth Embodiment

0096<figref idref="DRAWINGS">FIG. 4</figref> is a main part vertical portion showing the lens holding structure of the fourth embodiment. The lens holding structure shown in <figref idref="DRAWINGS">FIG. 4</figref> holds the lens <b>50</b> onto the inner surface <b>60</b><i>a </i>of the cylindrical lens <b>60</b> using a ring-like member <b>67</b> via a ring <b>69</b>.

0097The lens holding structure of <figref idref="DRAWINGS">FIG. 4</figref> has substantially the same structure as that of <figref idref="DRAWINGS">FIG. 3</figref>, except for the fact the lens is held by the ring-like member <b>67</b> using the middle ring <b>69</b>, and thus the parts that are the same have been assigned the same numbers and descriptions thereof have been omitted.

0098As shown in <figref idref="DRAWINGS">FIG. 4</figref>, the middle ring <b>69</b> which is an O-shaped ring made of resin is disposed at the ring-shaped corner portion <b>53</b><i>d </i>which is positioned at the boundary between the convex portion <b>51</b><i>a </i>of the lens portion <b>51</b> and the concave portion <b>53</b><i>a </i>of the outer peripheral portion <b>53</b>, and the middle ring <b>69</b> is pressed by the inner peripheral portion <b>68</b> of the ring-like member <b>67</b>.

0099In the case where the lens <b>50</b> is mounted and held in the lens barrel <b>60</b>, the lens <b>50</b> is inserted into the lens barrel <b>60</b> from the top of <figref idref="DRAWINGS">FIG. 4</figref> with the mounting portion <b>52</b> at the lower side thereof, and abuts the holding surface <b>62</b> of holding portion <b>61</b> of the lens barrel <b>60</b>. Next, the middle ring <b>69</b> is inserted into lens barrel <b>60</b> so as to fit onto the ring-like member <b>67</b> after being placed on the corner portion <b>53</b><i>d </i>of the lens <b>50</b> from the top of <figref idref="DRAWINGS">FIG. 3</figref>, and the middle ring <b>69</b> which is on the lens <b>50</b> is pressed by the ring-like member <b>67</b>.

0100Because of this configuration, the lens <b>50</b> can be held between the holding member <b>61</b> of the lens barrel <b>60</b> and the ring-like member <b>67</b> via the middle ring <b>65</b>, but due to the lens holding structure of <figref idref="DRAWINGS">FIG. 4</figref>, even if there is a temperature change of the lens barrel <b>60</b> due to the environment in which it is used, because the lens <b>50</b> is only pressed via the middle ring <b>69</b> by the ring-like member <b>67</b> from the upper portion of the drawing, the lens <b>50</b> can expand substantially freely due to the temperature change, and concentration of the stress caused by temperature change on the lens portion <b>51</b> becomes unlikely and stress generated due to temperature change is reduced. In this manner, generation of internal stress at the lens portion <b>51</b> is suppressed and change in the internal refractive index is controlled.

0101The ring-like member <b>67</b> is pressed on the lens <b>50</b> via the middle ring <b>69</b> which is disposed at the corner portion <b>53</b><i>d </i>of the lens <b>50</b>, and this even if there is a temperature change, shifting of the optical axis of the lens <b>50</b> in the lens barrel <b>60</b> is prevented. In addition, because the middle ring <b>69</b> is made of a resin, there is little shape deformation due to temperature change, and thus the center position of the lens <b>50</b> is more accurate.

0102It is to be noted that the middle ring <b>69</b> is preferably formed of a material that is not too hard and not too soft, such as a fluorine resin for example. The outer diameter of the outermost periphery <b>14</b> of the lens <b>10</b> is smaller than the inner diameter of the lens barrel <b>20</b> such that the lens <b>10</b> can be loosely fit into the lens barrel <b>20</b>.

Fifth Embodiment

0103Next, the bi-directional optical communication module in which the lens is fixed by the lens holding structure of <figref idref="DRAWINGS">FIG. 1</figref> is described with reference to <figref idref="DRAWINGS">FIG. 10</figref>. <figref idref="DRAWINGS">FIG. 10</figref> is a pattern diagram of the inside of the bi-directional optical communication module of the fifth embodiment viewed from the side surface.

0104As shown in <figref idref="DRAWINGS">FIG. 10</figref>, a bidirectional optical communication module <b>70</b> has a plastic lens <b>74</b> disposed inside a cylindrical case <b>71</b> which is formed form steel or Kovar (trade name). A hollow cylindrical holding body <b>72</b> is mounted at the left end of the case <b>71</b> in the figure and the optical fiber <b>73</b> is inserted through the inside thereof. Transmission of optical signal that are sent from and received by other terminals is possible because the optical fiber <b>73</b> is connected to an optical communication system, and the signal receiving beam b<b>1</b> exits and the signal emitting beam b<b>0</b> enters at the end surface <b>73</b><i>a. </i>

0105Furthermore, the base <b>77</b> is mounted at the right end of case <b>71</b> in the figure, and a light receiving element <b>78</b> formed of photodiode, and a light emitting unit <b>79</b> is mounted at the inside surface of the base <b>77</b>. The light emitting diode unit <b>7</b> includes a light emitting diode <b>79</b><i>a </i>which is a semiconductor laser and a glass lens <b>79</b> which are formed as one unit. The light receiving element <b>78</b> and the light emitting diode <b>79</b><i>a </i>are connected to an external terminal device (not shown) which can transmit electrical signals via the connector pin <b>77</b><i>a </i>which is planted on the base <b>77</b>.

0106The lens <b>74</b> has substantially the same structure as that of <figref idref="DRAWINGS">FIG. 1</figref> and is made up of an optical section <b>75</b> which has a lens function and a diffracting function; an outer peripheral portion <b>76</b><i>a </i>which is positioned on the outer peripheral side of the optical section <b>75</b> and extends to the outermost periphery of the lens <b>74</b>; and is fixed with an bonding agent to the holding portion <b>71</b><i>a </i>which protrudes from the inner surface of the case <b>71</b> using the mounting portion <b>76</b>, and is bonded and fixed using the same lens holding structure as in <figref idref="DRAWINGS">FIG. 1</figref>. One surface of the optical section <b>75</b> is formed such that the diffraction grating <b>75</b> which has a 4-step configuration is cyclically repeated.

0107The signal receiving beam b<b>1</b> becomes a first order refracting beam at the diffraction grating <b>75</b><i>a </i>(shown by the broken line in the figure) and is focused on the light receiving surface of the light receiving element <b>78</b> and converted to electrical signals. The signal emitting beam b<b>0</b> sent from the light emitting diode unit <b>79</b> is passed directly as a zero order refraction transmission beam (shown by the solid line) at the diffraction grating <b>75</b><i>a</i>, and then entered on the end surface <b>73</b><i>a </i>of the optical fiber <b>73</b> and passed through the optical fiber <b>73</b> and sent to the outside. The wavelength of the signal receiving beam b<b>1</b> is 1.49 μm and the wavelength of the signal emitting beam b<b>0</b> is 1.31 μm for example. As described above, the signal receiving beam b<b>1</b> which is first order refraction beam and the signal emitting beam b<b>0</b> which is the zero order refraction beam and which have different wavelengths are separated at the diffraction grating <b>75</b><i>a. </i>

0108With the bidirectional optical communication module <b>70</b>, when the temperature at which the device is used changes within a range from room temperature to 85° C., the stress generated due to difference in expansion and contraction of the lens <b>74</b> that is formed from plastic and the case <b>71</b> that is formed from metal can be limited potions other than the optical section <b>75</b> like the mounting portion <b>76</b>, and thus stress generation at the optical section <b>75</b> becomes difficult. As a result deformation of the optical section <b>75</b> is controlled, deterioration of the optical properties of the optical section <b>75</b> is controlled and shifting of the optical axis of the lens <b>74</b> is prevented. Thus even if the optical communication module <b>70</b> is used in an environment where there are temperature changes, deterioration in the capacity of the optical communication module to send and receive signals is controlled.

Sixth Embodiment

0109Next another example of the bidirectional optical communication module in which the lens is fixed by the lens holding structure of <figref idref="DRAWINGS">FIG. 1</figref> is described with reference to <figref idref="DRAWINGS">FIG. 11</figref>. <figref idref="DRAWINGS">FIG. 11</figref> is a pattern diagram of the inside of the bidirectional optical communication module of the sixth embodiment viewed from the side surface.

0110The optical communication module <b>80</b> of <figref idref="DRAWINGS">FIG. 11</figref>, is formed in the case <b>80</b><i>a </i>such that the signal receiving beam c from the optical transmission path of the optical communication system is entered from the end surface of the optical fiber <b>81</b> and then passed through the wavelength splitting filter <b>82</b>, and then passed through the collimator lens <b>86</b> and then received at the light receiving element <b>83</b>. In addition, signal emitting beam d from the light emitting diode <b>84</b> passes through collimator lens <b>89</b> and is reflected at the wavelength splitting filter <b>82</b> and entered onto the end surface of the optical fiber <b>81</b>, and then sent on the optical transmission path of the optical communication system.

0111Each of the collimator lens <b>86</b> and <b>89</b> have substantially the same structure of those of <figref idref="DRAWINGS">FIG. 1</figref> and comprises an optical sections <b>86</b><i>a </i>and <b>89</b><i>a </i>which have a lens function; and mounting portions <b>86</b><i>b </i>and <b>89</b><i>b </i>which are on the outer peripheral side of the optical sections <b>86</b><i>a </i>and <b>89</b><i>a </i>and extend in the direction of the respective optical axis; and are fixed by bonding to respective the holding portions <b>85</b><i>a </i>and <b>88</b><i>a </i>which protrudes from the lens barrels <b>85</b> and <b>88</b> using the mounting portion <b>86</b><i>b </i>and <b>89</b><i>b</i>. In <figref idref="DRAWINGS">FIG. 11</figref>, lens barrels <b>85</b> and <b>88</b> are formed metals such as steel or Kovar (trade name) and the collimator lens <b>86</b> and <b>89</b> are from plastic.

0112With the bidirectional optical communication module <b>80</b>, when the temperature at which the device is used changes within a range from room temperature to 85° C., the stress generated due to difference in expansion and contraction of the collimator lens <b>86</b> and <b>89</b> that are formed from plastic and the lens barrels <b>85</b> and <b>88</b> that are formed from metal can be limited to portions other than the optical sections <b>86</b><i>a </i>and <b>89</b> such as the mounting portions <b>86</b><i>b </i>and <b>89</b><i>b </i>of the collimator lens <b>86</b> and <b>89</b> and thus stress generation at the o optical sections <b>86</b><i>a </i>and <b>89</b><i>a </i>becomes difficult. As a result deformation of the optical sections <b>86</b><i>a </i>and <b>89</b><i>a </i>is controlled, deterioration of the optical properties of the optical sections <b>86</b><i>a </i>and <b>89</b><i>a </i>is controlled and shifting of the optical axis of the collimator lens <b>86</b> and <b>89</b> is prevented. Thus even if the optical communication module <b>80</b> is used in an environment where there are temperature changes, deterioration in the capacity of the optical communication module to send and receive signals is controlled.

Working Example

0113The following is a description of this invention using a working example, but this invention is not to be limited by this working example. This working example uses a lens holding portion that is substantially similar to that of <figref idref="DRAWINGS">FIG. 1</figref>, and it fixes the plastic lens shown in <figref idref="DRAWINGS">FIG. 5</figref> inside the lens barrel. The lens barrel is made of steel.

0114The plastic lens of <figref idref="DRAWINGS">FIG. 5</figref> is fixed by a bonding agent at 70° C. in the lens barrel shown in <figref idref="DRAWINGS">FIG. 1</figref>, and deformation of the entire lens when the temperature returns to room temperature (25° C.) is shown in <figref idref="DRAWINGS">FIG. 6</figref>. Next the results of calculating the refractive index change at various temperatures (−40° C., 25° C., 85° C.) and internal stress generated at the plastic lens of <figref idref="DRAWINGS">FIG. 5</figref> is shown in <figref idref="DRAWINGS">FIG. 8</figref>. The distribution of the diffraction rate change (stress) at the lens portion plastic lens at this time is shown in <figref idref="DRAWINGS">FIG. 7</figref>. The distribution in <figref idref="DRAWINGS">FIG. 7</figref> is shown by color, and the colors in <figref idref="DRAWINGS">FIG. 7</figref> correspond to the colors shown on the bar in <figref idref="DRAWINGS">FIG. 8</figref>, and the colors on the bar of <figref idref="DRAWINGS">FIG. 8</figref> correspond to the refraction rate change (stress) in the chart in <figref idref="DRAWINGS">FIG. 8</figref>.

0115From <figref idref="DRAWINGS">FIG. 6</figref>, it is seen that the plastic lens that is fixed inside the lens barrel is formed by the bonding agent layer and the portion in the vicinity thereof and this deforms, but the lens portion does not deform that much. Also, from <figref idref="DRAWINGS">FIGS. 7 and 8</figref>, it is seen that the distribution of the refractive index changes (stress) at the lens portion of the plastic lens only changes slightly at the vicinity of the outer periphery side, and thus there is no substantial change and the distribution is mostly even.

0116<figref idref="DRAWINGS">FIG. 12</figref> shows the relationship between the optical light path difference and the radial position from the lens center when the plastic lens in <figref idref="DRAWINGS">FIG. 5</figref> is at each of the temperatures −40° C., 25° C., and 85° C. From <figref idref="DRAWINGS">FIG. 12</figref>, it is seen that the optical light path difference does not depend on the radial position when the temperature is −40° C., 25° C., and is substantially fixed, and in the outer circumference vicinity of the lens portion changes slightly when the temperature is 85° C. But the internal refraction index change due to changes in stress is within a practical range.

0117The expansion and contraction in the range of the temperature for use (0-85° C.) when the plastic lens of <figref idref="DRAWINGS">FIG. 5</figref> is held and fixed in the lens barrel with a bonding agent as in <figref idref="DRAWINGS">FIG. 1</figref>, is approximately 20 μm, but the accuracy of the center position is less than 1 μm and generation of stress at the lens portion is prevented. From <figref idref="DRAWINGS">FIG. 14</figref>, it is seen that if the shifting of the center position is less than 1 μm, there is little or no effect on output movement. It is to be noted that the Young's modulus, the linear expansion coefficient, and the Poisson number of the resin (plastic), the bonding agent and the steel respectively are as shown in Table 1. It is to be noted that in Table 1, “E-j” represents “10^−j” (this is the same for <figref idref="DRAWINGS">FIGS. 8 and 9</figref> also).

0118<tables id="TABLE-US-00001" num="00001"><table frame="none" colsep="0" rowsep="0"><tgroup align="left" colsep="0" rowsep="0" cols="4"><colspec colname="offset" colwidth="77pt" align="left" /><colspec colname="1" colwidth="49pt" align="left" /><colspec colname="2" colwidth="49pt" align="left" /><colspec colname="3" colwidth="42pt" align="left" /><thead><row><entry /><entry namest="offset" nameend="3" rowsep="1">TABLE 1</entry></row><row><entry /><entry namest="offset" nameend="3" align="center" rowsep="1" /></row><row><entry /><entry>Bonding</entry><entry /><entry /></row><row><entry /><entry>agent</entry><entry>Resin</entry><entry>Steel</entry></row><row><entry /><entry namest="offset" nameend="3" align="center" rowsep="1" /></row></thead><tbody valign="top"><row><entry /></row></tbody></tgroup><tgroup align="left" colsep="0" rowsep="0" cols="5"><colspec colname="offset" colwidth="14pt" align="left" /><colspec colname="1" colwidth="63pt" align="left" /><colspec colname="2" colwidth="49pt" align="left" /><colspec colname="3" colwidth="49pt" align="left" /><colspec colname="4" colwidth="42pt" align="left" /><tbody valign="top"><row><entry /><entry>Young's modulus</entry><entry>2.2 GPa</entry><entry>3.2 GPa</entry><entry>208 GPA</entry></row><row><entry /><entry>Linear expansion</entry><entry>1.50E−04</entry><entry>6.00E−05</entry><entry>1.1.8E−05</entry></row><row><entry /><entry>coefficient</entry></row><row><entry /><entry>Poisson Number</entry><entry>0.36</entry><entry>0.36</entry><entry>0.29</entry></row><row><entry /><entry namest="offset" nameend="4" align="center" rowsep="1" /></row></tbody></tgroup></table></tables>

0119Preferred embodiments and a working example of the present invention have been described above but these are not intended to limit the invention and various modifications may be made without technologically departing from the spirit of the invention. For example, in <figref idref="DRAWINGS">FIG. 1-FIG</figref>. <b>4</b>, the optical element that is to be held is a lens, but the invention is not limited thereto and, as a matter of course, the object to be held may be an optical element other than lens, such as a diffraction grating or an optical element having both a lens function and a diffraction function.

0120One lens portion of the lens in <figref idref="DRAWINGS">FIG. 1-FIG</figref>. <b>4</b> is convex surface, while the other is a flat surface, but the invention is not limited to this configuration, and both may be convex surfaces, or alternatively one surface may take a form like a diffraction grating.

0121Also, in <figref idref="DRAWINGS">FIG. 1-FIG</figref>. <b>4</b>, the mounting portion extends in a substantially parallel direction with respect to optical axis, but the invention is not limited to this configuration, and the mounting portion may incline with respect to the optical axis.